The present invention relates to high-capacity, thin and highly conformable absorbent structures, useful in absorbent articles including baby diapers, adult incontinence products, sanitary napkins and the like. More particularly, the present invention relates to absorbent structures containing matrix fibers, binders and superabsorbent polymers, the structure having an x-directional fluid storage profile.
Absorbent structures are important in a wide range of disposable absorbent articles including baby diapers, adult incontinence products, sanitary napkins and the like.
These and other absorbent articles are generally provided with an absorbent core to receive and retain body liquids. The absorbent core is usually sandwiched between a liquid pervious topsheet, whose function is to allow the passage of fluid to the core and a liquid impervious backsheet whose function is to contain the fluid and to prevent it from passing through the absorbent article to the garment of the wearer of the absorbent article.
An absorbent core for diapers and adult incontinence pads frequently includes fibrous batts or webs constructed of defiberized, loose, fluffed, hydrophilic, cellulosic fibers. The core may also include superabsorbent polymer (xe2x80x9cSAPxe2x80x9d) particles, granules, flakes or fibers (collectively xe2x80x9cparticlesxe2x80x9d).
In recent years, market demand for an increasingly thinner and more comfortable absorbent article has increased. Such an article may be obtained by decreasing the thickness of the diaper core, by increasing the amount of SAP particles, and by calendaring or pressing the core to reduce caliper and hence, increase density.
However, higher density cores do not absorb liquid as rapidly as lower density cores because densification of the core results in a smaller effective pore size. Accordingly, to maintain suitable liquid absorption, it is necessary to provide a low-density layer having a larger pore size above the high-density absorbent core to increase the rate of uptake of liquid discharged onto the absorbent article. The low-density layer is typically referred to as an acquisition layer. Multiple layer absorbent core designs involve a more complicated manufacturing process.
The storage layer portion of a disposable diaper for example, is generally formed in place, during the converting process, from loose, fluffed cellulose. Such cellulose material is generally not available in preformed sheet form because it exhibits insufficient web strength, owing to its lack of interfiber bonding or entanglement, to be unwound or unfestooned directly onto and handled in absorbent pad-making equipment.
Some absorbent articles such as ultra-thin feminine napkins are generally produced from roll-goods based nonwoven material. Such a roll of preformed absorbent core material is unwound directly as feedstock into the absorbent article converting equipment without the defiberization step normally required for fluff-based products, such as diapers and incontinence pads. The nonwoven web is typically bonded or consolidated in a fashion that gives it sufficient strength to be handled during the converting process. Absorbent structures made from such nonwoven webs may also contain SAP particles. However, these absorbent structures are often inefficient in cases where a demand is for acquisition and absorption of high amounts or a surge of body fluids. In these cases, a single sheet absorbent material often is not sufficient to fully utilize the absorbent core because the liquid is not distributed in the structure along the length of the absorbent core. As a result, regions of the absorbent core remain unused.
The web consolidation mechanism used in the roll-goods approach to making preformed cores provides strength and dimensional stability to the web. Such mechanisms include latex bonding, bonding with thermoplastic or bicomponent fibers or thermoplastic powders, hydroentanglement, needlepunching, carding or the like. However, such bonded materials provide a relatively stiff core which often does not conform well to the shape of the human body, especially in those situations where there is a demand for good fit to acquire and contain high volumes of body fluids.
Pliability and softness of the absorbent core are necessary to ensure that the absorbent core can easily conform itself to the shape of the human body or to the shape of a component (for example another absorbent ply) of the absorbent article adjacent to it. This in turn prevents the formation of gaps and channels between the absorbent article and the human body or between various parts of the absorbent article, which might otherwise cause undesired leaks in the absorbent article.
Integrity of the absorbent core is necessary to ensure that the absorbent core does not deform and exhibit discontinuities during its use by a consumer. Such deformations and discontinuities can lead to a decrease in overall absorbency and capacity, and an increase in undesired leakages. Prior absorbent structures have been deficient in one or more of pliability, integrity, profiled absorbency and capacity. For example, a conventional (fluff pulp) core has good conformability because of its high pliability and softness but at the same time it may disintegrate easily during use, due to its poor integrity. As another example, certain bonded cores, such as airlaid cores made from cellulose fluff pulp densified to greater than 0.35 g/cc have good dry integrity, but have poor wet integrity and poor conformablity.
The absorbent materials described herein exhibit a superior combination of x-directional storage profile, conformability and integrity. This combination provides improved fluid acquisition and containment as well as increased comfort and reduced leakage potential. Further, the improved integrity of the disclosed absorbent materials reduces the risk of deformation of the absorbent material and better protects the surface of the skin of the user from exposure to liquid.
The present invention relates to an absorbent structure having wet integrity higher than about 4.0 kN/gsm, softness higher than 8.0/J, pliability higher than about 70/N, and providing a substantially dry liquid-accepting surface after receiving a quantity of liquid. The structure includes an upper ply having an upper fluid receiving surface and a lower surface and including a top stratum including synthetic matrix fibers bonded with a binder, the matrix fibers having length from about 2 to about 15 mm; a middle stratum in fluid communication with the top stratum, the middle stratum including natural fibers, superabsorbent particles and a binder; and a bottom stratum in fluid communication with the middle stratum, the bottom stratum including natural fibers and a binder. The structure also includes a lower ply in fluid communication with the upper ply, the lower ply having an upper surface and a lower surface and including at least one stratum including natural fibers, superabsorbent polymer particles, and a binder, wherein the lower surface of the upper ply has a surface area less than about 80% of the upper surface area of the lower ply.